In a typical installation, a number of horizontally oriented surfaces or trays are mounted in a sealed, vertically oriented vessel known in the industry as a column or tower. Each of the trays may contain numerous openings. A relatively heavier fluid is introduced on the upper surface of the uppermost tray deck. The introduction of this fluid at one end of the horizontal tray is referred to as the upstream end or portion. A crossflow forms as the fluid flows across from the upstream end of the tray to the downstream end or portion of each tray. At the downstream end of the tray is a weir which leads to a downcomer. The downcomer of an upper tray leads down to an unperforated upstream area or downcomer seal area on the next lower tray.
A lighter gas or fluid is introduced into the lower end of the column. As the heavier liquid or fluid flows across the tray surface, the lighter gas ascends through the openings in the trays and into the heavier liquid flowing across and above the surface of the tray. This creates a bubble or active area where there is intimate and active contact between the heavier and lighter fluids. Some columns utilize multiple sets of flow paths including a downcomer, active area and downcomer seal transition area for each section.
Many crossflow trays are simple sieve trays where the deck surface has hundreds of circular holes for contact between the fluids. However, a simple hole such as this type of aperture or opening allows for the lighter fluid to shoot straight up and hit the bottom of the above tray deck. This is commonly referred to as flooding and greatly decreases the efficiency and capacity of the entire column and may introduce impurities into the fractionation process.
To combat flooding, some trays have valves associated within the tray openings and others have fixed assemblies over the holes or apertures. The valves may have different configurations to deflect the rising gases. These valves rise upwardly and fall due to gravity by the introduction of fluid pressure from below the valve. However, while each valve deflects the vapor flow from shooting up and flooding the tray deck, each individual valve introduces a small area of blockage across the each aperture of the tray deck thereby reducing the interaction or exchange between the fluids. This small, central area above each valve is a stagnant zone or an inactive area where minimal mass transfer exchange occurs.
It has already been proposed in, for example, U.S. Pat. No. 4,118,446, dated Oct. 3, 1978, by Burin et al., (Col. 4, 11. 44-45), to provide perforations in upwardly movable valve cover plates, for tray openings, to eliminate stagnant zones in a mass exchange column containing valve trays at different heights therein. A relatively lighter fluid is fed into the column beneath the trays to flow upwardly through the openings, while heavier fluid is fed into the column above the trays. The heavier fluid gravitates down the column by passing across each tray while the lighter fluid ascends in the tray lifting the valve cover plates and causing intimate contact between the fluids. The Burin et al. perforations are provided to eliminate stagnant zones in the heavier fluid flowing immediately above the caps.
While the Burin et al. valve perforations to some extent eliminate stagnant zone, there is a problem in that bubbles from lighter fluid flowing upwardly from the perforations and through the stagnant zones tend to follow definite paths through the heavier fluid leaving portions of the stagnant areas undisturbed. Additionally, these types of perforations will allow the lighter gas carrying heavier liquid, commonly referred to as entrainment, to shoot straight up to the bottom of the upper tray thereby causing premature flooding and lowering the efficiency and capacity of the column.
U.S. Pat. No. 3,215,414, dated Nov. 2, 1965, by Van't Sant (col. 1, lines 48-51 and col. 3, lines 3-6), shows a valve cover plate having opposed recesses into which an arched guide band is clipped to extend over the valve cover plate and downwardly through the recesses to guide the valve during when it is lifted by upwardly flowing fluid. Partial closure of the valve allows minimum free passage of fluid between the cover plate and the tray at all times. While the guide band of Van't Sant is useful in providing the easily assembled, two part valve body that it was intended to do, any fluid escaping upwardly under the guide band will be minimal and will not be directed towards the central stagnant zone over the valve cover plate leaving this zone undisturbed.
There is a need for a fluids contacting, tray opening, fluid dispersing assembly, wherein fine or micro dispersion of the lighter fluid is achieved over the central portion of the cover plate, thus more effectively breaking up the stagnant zone above the individual valves and enhancing mass transfer between the fluids as well as increasing the column handling capacity and efficiency.